I could go on about how Castlevania (Or "C-") Alucard is merely a dhampir or a human-vampire hybrid, being born from a human mother... which could be C-Alucard's greatest battle ability in itself. There are many different tales of lore about dhampirs that all have one consistency: they have all of a vampire's strengths, but none of their weaknesses...

Hellsing (or "H-") Alucard is the opposite: a full-fledged vampire with a bloodlust to match. Though they are worlds apart in combat abilities (C-Alucard uses a magically-enhanced silver short sword, while H-Alucard uses custom-made high-caliber pistols), the real battle is one of their bodily resistances. H-Alucard cannot be killed by any standard means; staking through the heart, decapitation, sunlight... none will work, whereas a wound in a vital spot will ultimately kill C-Alucard... however, it can be assumed that H-Alucard has one major weakness of the original Dracula (holy artifacts, of which C-Alucard has none).

I give this fight to Hellsing's Alucard, if only for being so bloody overpowered that it's not even a fair fight anymore.